1. Field of the Invention
The invention relates to a control apparatus for an internal combustion engine that uses a low-volatility fuel, for example, alcohol fuel, and relates to a control method for the internal combustion engine control apparatus.
2. Description of Related Art
As a related-art technology, there is known a control apparatus for an internal combustion engine that uses alcohol fuel as disclosed in, for example, Japanese Patent Application Publication No. 2007-224878 (JP-A-2007-224878). Since the alcohol fuel less readily vaporizes particularly at low temperature, the related-art internal combustion engine is provided with a vaporization chamber for vaporizing the fuel at the time of starting the engine. This vaporization chamber has a sealed structure that is isolated from the outside, and is connected to an intake passageway via a throttle passageway. Besides, the vaporization chamber is provided with an engine-start fuel injection valve that injects fuel into the vaporization chamber, and with a heater for heating the injected fuel.
To start the internal combustion engine, the heater is firstly activated at the time point at which a start signal is output to the internal combustion engine. After that, at the time point of elapse of an appropriate amount of time, the fuel is injected from the engine-start fuel injection valve into the vaporization chamber. When the fuel is injected, the vaporization chamber enters a reduced-pressure state due to intake negative pressure caused by cranking. As a result, the injected fuel vaporizes by receiving heat from the heater within the vaporization chamber under reduced pressure, and is supplied to each cylinder through the intake passageway. Thus, the related-art technology is intended to secure good engine startability during a cold start state or the like by vaporizing the fuel in the vaporization chamber at the time of starting the engine.
In the foregoing related-art technology, at the time of starting the engine, the heater is activated before the fuel is injected into the vaporization chamber to produce vaporized fuel. However, in this technology, after the engine start signal is output to the internal combustion engine, the heating of the heater and the heating of the injected fuel as well as the pressure reduction of the vaporization chamber are performed, so that the vaporized fuel is produced. Therefore, in the related-art technology, the production of the vaporized fuel at the time of start of the engine may require time, and it may not be possible to promptly supply the vaporized fuel into the cylinders.
Besides, the related-art technology does not have a construction for accurately grasping the air/fuel ratio in the vaporization chamber. Therefore, depending on the concentration of the vaporized fuel supplied to the engine at the time of start thereof, the air/fuel ratio at the time of start may be deviated to a lean side or a rich side, leading to a concern about deterioration of engine startability and deterioration of emission quality.